The present invention relates to a method of manufacturing curveable reinforcement having open regions and intended for reinforcing a section member, in particular for making gaskets for motor vehicles.
By way of example, the type of reinforced gasket presently manufactured is made up of:
a) rigid metal reinforcement, e.g. of channel section (cut out from steel or aluminum, or sheared and drawn, or indeed of steel wire with textile);
b) a covering of flexible thermoplastic or rubber; where necessary the reinforcement is treated so as to make it adhere to the covering;
c) fastening lips inside the channel section; and
d) a flexible portion that provides sealing, made of flexible or cellular rubber.
The major drawbacks of the method presently in use are as follows:
The metal of the extruded section members must be preformed or post-formed.
The metal oxidizes at the ends of the section member. To avoid oxidation, it is necessary to provide protection. In which case, a stainless metal is used or else varnish is deposited on the portions exposed to oxidation. That significantly increases the price of the finished product.
The finished product is difficult to recycle because it is made up of multiple materials of different kinds (metal, rubber, thermoplastic).
Manufactured metal is expensive, and its cost is even higher if the metal needs to be prepared in order to make it adhere to the covering of rubber or of thermoplastic.
Material is necessarily lost because of the need to make cutouts.
The weight of metal reinforcement is considerable, with the specific gravity of aluminum being 2.7 and of steel being 7.8.
It is necessary to prepare the ends in order to be able to bond them or to overmold them (unhooking, trimming).
At least some of the above drawbacks are avoided by the method of the invention based on the idea of making the reinforcement of out thermoplastic material (whose specific gravity lies in the range 0.9 to 1.4 depending on the material chosen).
The invention thus provides a method of manufacturing curveable reinforcement presenting a pattern comprising solid portions and open portions and intended for use in making a reinforced sealing section member, the method comprising:
a) extruding a bead or preform of thermoplastic material; and
b) calendering the bead or preform of thermoplastic material to impart said pattern thereto.
During the calendering, the plastics material is in a fluid or semi-fluid state and presents viscosity which enables it to flow so as to make the solid portions and the open portions of the desired pattern(s). As a result, the reinforcement is obtained without having to perform any cutting out which would imply removing material.
The method may comprise:
c) cooling the calendered bead or preform.
The cooling may be accompanied by a calibration operation.
The curveable reinforcement may present a section that is U-shaped, V-shaped, S-shaped, L-shaped, or W-shaped.
In a first variant, the calendering is performed between at least two wheels, at least one of which presents recessed imprints in the shape of said pattern, which wheels are driven to rotate simultaneously. At least one of the wheels can be cooled internally.
In a preferred variant, the calendering is performed by means of a pulling caterpillar having N pairs of shapes presenting imprints in the shape of said pattern.
Advantageously, the calendering wheels or the drawing caterpillar presents a developed length that is equal to or a multiple of the length L of a section member to be made. This makes it possible in particular to make reinforcement whose pattern presents variations, e.g. in thickness or in the position of the neutral axis as a function of an abscissa x taken in the long direction of the reinforcement, x varying over the range 0 to L, in order to vary the section and thus at least one of the properties of the reinforcement as a function of said abscissa.
The reinforcement may have end branches with side edges that slope so as to form tapers.
In order to make a reinforced sealing section, the method may comprise:
d) extruding a flexible covering layer of elastomer or of a thermoplastic material to cover the reinforcement.
This extrusion of a covering layer can be performed immediately after calendering and cooling, such that the sealing section is obtained by a continuous process. In a variant, the reinforcement can be stored after manufacture, e.g. on a drum, after which the operation of extruding the covering layer can be performed on a distinct installation.
In the method, the rigid reinforcing material and the material of the flexible cover layer are for example: rigid polyvinyl chloride (PVC) and flexible PVC; polypropylene (PP) and polypropylene-ethylene-propylene diene monomer (PP-EPDM) or styrene-ethylene butadiene-styrene (SEBS); acrylonitrile butadiene styrene (ABS) and SEBS; PVC-ABS and flexible PVC; and polymethyl methacrylate (PMMA) and SEBS.
The method may implement coextrusion of an intermediate layer and of the layer of covering material, the intermediate layer being of a material that is suitable for adhering to the material of the reinforcement and to the flexible covering material between which it is interposed.
By way of example, the intermediate layer may be selected from ethylene vinyl acetate (EVA) copolymers or ethylene-acrylic ester copolymers (EMA EBA).
In a preferred implementation with an intermediate layer, the reinforcement is made of polyamide (PA), the intermediate layer is made of maleic anhydride grafted epoxy (EP), and the flexible covering layer is made of EPDM.
The invention also provides curveable reinforcement having a pattern with solid portions and open portions at least in a dorsal region, wherein the open portions of the dorsal region present web regions that are thin relative to the solid portions and that form bridges between the solid portions of the dorsal region.
Outside the dorsal region, the solid portions of the reinforcement may optionally present branches including reentrant edges.
Finally, the invention provides a section member including reinforcement as defined above.